Cold Spells and Heat Both Raise Heart Failure Hospitalization Risk, Study Finds

Heart failure hospitalizations rise after short bouts of cold weather and after both lower and higher ambient temperatures, according to a study published in the Journal of the American College of Cardiology (JACC) and presented at ESC Congress 2026. Researchers analyzed 482,000 heart failure hospitalizations recorded in the Swedish National Patient Register between 2006 and 2021.

The team, led by Wenli Ni, Ph.D., a postdoctoral fellow at Harvard T.H. Chan School of Public Health's Center for Climate, Health, and the Global Environment, defined cold spells as two or more consecutive days at or below the local 5th percentile temperature between October and March, and heat waves as two or more days at or above the local 95th percentile between April and September. Ni said no previous study had examined these short-term links in a Nordic population, noting Sweden faces frequent cold exposure along with a rising, unacclimatized vulnerability to heat as the climate warms.

Cold spells were linked to a higher hospitalization risk within two to six days, reaching statistical significance between three and five days. Lower ambient temperatures overall showed a similar pattern, with risk elevated within three to six days and significant between three and five days. Higher ambient temperatures, by contrast, were linked to higher hospitalization risk over a shorter window of zero to three days. Heat waves specifically showed no association with heart failure hospitalization.

The authors said the delayed risk after cold exposure and the immediate risk after heat point to a need for time-sensitive responses, including monitoring patients after cold alerts and more urgent action during hot spells.

In an accompanying editorial, Tiantian Li, Ph.D., deputy director of the National Institute of Environmental Health at the Chinese Center for Disease Control and Prevention in Beijing, wrote that evidence linking non-optimal temperature to cardiovascular harm is now substantial, and said the field must move from accumulating associations to building an actionable early-warning capability.